Glass coated electrical steel sheet and articles prepared therefrom

ABSTRACT

An oriented silicon steel product and method for producing the same is described in which improved magnetostriction and strain sensitivity are obtained by means of bonding a thin glass layer to the surface of the steel.

nite States Patent [191 Foster et a1.

[ 1 Sept. 17, 1974 GLASS COATED ELECTRICAL STEEL SHEET AND ARTICLESPREPARED THEREFROM [75] Inventors: Karl Foster; Joseph Seidel, both ofPittsburgh, Pa.

[73] Assignee: Westinghouse Electric Corporation,

Pittsburgh, Pa.

22 Filed: Mar.22, 1972 21 Appl. No.: 237,202

Related US. Application Data [60] Continuation of Ser. No. 46,152, June15, 1970, abandoned, which is a division of Ser. No. 576,963, Sept. 2,1966, Pat. No. 3,528,863, which is a continuationin-part of Ser. No.556,337, June 9, 1966, abandoned.

[52] US. Cl 1117/129, 117/70 A, 106/48,

106/54 [51] int. Cl. C03c 7/02, C03C 7/04, C03c 3/08 [58] Field ofSearch 106/54, 48; 117/129, 230,

Primary Examiner winston A. Douglas Assistant Examiner--Mark BellAttorney, Agent, or FirmR. T. Randig [5 7 ABSTRACT An oriented siliconsteel product and method for producing the same is described in whichimproved magnetostriction and strain sensitivity are obtained by meansof bonding a thin glass layer to the surface of the steel.

2 Claims, 4 Drawing Figures GLASS COATED ELECTRICAL STEEL SHEET ANDAlR'llllClLES PREPARED THEREFROM CROSS-REFERENCE TO RELATED APPLICATIONThe present application is a continuation of application Ser. No. 46,152filed June 15, 1970, now abandoned, which in turn was a division ofapplication Ser. No. 576,963 filed Sept. 2, 1966, now US. Pat. No.3,528,863 which issued Sept. 15, 1970, which in turn was acontinuation-in-part of application Ser. No. 556,337 filed June 9, 1966,now abandoned.

This invention is directed to a process for producing oriented magneticsheet having an inorganic vitreous coating thereon for reducingmagnetostriction wherein the magnetic sheet to be coated has anintermediate coating of complex magnesium-base compounds thereon; to thecoated magnetic sheet made by the process; to articles such as coresmade by bonding the coated magnetic sheet; and to the special glasscompositions used in the process.

The electrical steel with which this invention is concerned is aniron-silicon alloy containing up to 6% silicon, by weight, and mostcommonly about 3% silicon. Electrical steels of this composition whenappropriately treated will assume preferred grain orientation ortextures. One oriented electrical steel sheet of this type has aso-called cube-on-edge grain orientation, or as it is moreconventionally identified in terms of Miller indices, the (110) [001]grain texture, and has attained great commercial importance. The singleoriented magnetic sheets of this type and magnetic cores made from thesesheets are often soldunder the trademark Hipersil.

Another oriented electrical steel sheet contains essentially the sameamount of silicon and has a cubeon-face" grain texture or double grainorientation, or, in Miller indices, a l)[001] texture. This doubleoriented material has also been produced in commercial quantities andoriented magnetic sheets of this type and magnetic cores made from themare sold under the trademark Cubex.

A typical composition of the above-mentioned oriented electrical steelsheets is; 3.15% silicon, about 0.1% manganese less than 0.005% each ofcarbon oxygen and sulfur and the balance essentially iron.

Transformers have laminations made from these silicon-iron single anddouble oriented steels perform very satisfactorily in most instances.However, transformers of this type do produce a substantial amount ofnoise during operation, as the result of the phenomenon known asmagnetostriction. Many materials when magnetized or demagnetized undergochanges in dimension, the effect called magnetostriction, which isdefined as:

A L/L or the change in length per unit length in the direction ofmagnetization under the magnetizing force applied, the ratio increasingwith increasing induction. The symbol )t is commonly employed torepresent this dimensional ratio. It is obvious that the reduction ofaudible noise produced by transformers is a goal of high desirability,in view of the ever-increasing trend toward loeating power sub-stationsclose to densely populated areas, in office and apartment buildings andin shop areas.

While, with the improvement in magnetic materials already achieved withrespect to core loss and permeability, it is quite feasible to operatetransformers at higher inductions than have been utilized in the past, alimitation is imposed by the noise generated by the transformers. Sincethe magnitude of the magnetostrictive effect, and the noise producedthereby, increases with the induction, in many cases it has beennecessary to operate transformers at a level below the maximum inductionat which they are capable of operating at a substantial economicsacrifice.

The magnetostrictive effect discussed above is extremely important intransformers of large size, transformers which are of the stackedlamination type. In making transformers of this type a magnetic sheet isstamped to the proper size and shape and the flat sheets are thenstacked to achieve a transformer core of the desired size.

In certain smaller cores of the wound-cut type also known as C-cores(the two halves ofa cut core being C-shaped), the problem of noise doesnot loom so large, but other problems do exist in this area because thepresently employed organic bonded C-cores are characterized byrelatively high core loss and, of course, are restricted to relativelylow service temperatures, of perhaps 200 or 250C., above which theresins presently used tend to deteriorate, with the result that the coredelaminates and may become substantially inoperative. The manufacture ofsuch organically bonded cores is a rather complex process requiring aplurality of steps which must be carefully carried out to obtain asatisfactory product.

Typically, the process for making organically bonded magnetic coresinvolves coating a magnetic strip material with an inorganic electricalinsulator such asmagnesium phosphate, winding the coated magnetic stripto core configuration, annealing the wound core to remove stressesintroduced in the winding process, impregnating the core with a bondingresin in a vacuum environment to obtain penetration of the resin betweenadjacent laminations, and oven curing the resin impregnated core toharden the resin and thereby bonded into an integral structure. Afterthe curing procedure the core is cut so that performed coils may beconveniently placed about the core. A less complex process would thusclearly be highly desirable.

It is therefore, an object of the present invention to reduce the noiselevel due to magnetostrictive effects in induction apparatus such astransformers by employing sheets of electrical steel having a compositecoating thereon which maintains the steel sheet in tension therebyreducing magnetostriction and strain sensitivity.

It is a further object of the invention to provide for use as coatingson magnetic steel sheet, glass compositions having coefficients ofthermal expansion substantially less than that of the steel sheet andcapable of flowing to coat the steel sheet in a temperature range inwhich the stress relief of the steel sheet can be concurrentlyaccomplished, whereby on cooling the steel sheet is held in tension bythe glass coating.

It is still another object of this invention to provide a process formaking oriented electrical steel sheets having extremely lowmagnetostrlction which includes providing a composite coating on thesteel sheets wherein a thin, highly adherent glass coating is bonded tothe steel sheet through an intermediate layer of complex magnesium-basecompounds.

Another object of this invention is to provide a glass coated orientedelectrical steel sheet wherein the glass coating maintains the steelsheet in tension to thereby reduce magnetostrictive effects and whereinthe glass coating is bonded to the steel sheet through an intermediatelayer of complex magnesium-base-compounds.

It is another object of this invention to provide a glass bonded corestructure comprising a plurality of electrical steel sheets each havingthereon an intermediate layer of complex magnesium-base compounds, theglass being bonded to adjacent steel sheets through the saidintermediate layer and forming an insulating layer between adjacentsteel sheets.

Another object of the invention is to provide a bounded wound and cutmagnetic core wherein adjacent turns of the core are bonded to eachother by a thin, highly adherent layer of glass disposed between theturns, the glass being bonded to the steel sheet through an intermediatelayer of complex magnesiumbase compounds; the glass providing insulationbetween the said adjacent turns and bonding the structure into anintegral whole.

Other objects of the invention, will, in part, be obvious and will, inpart, appear hereinafter.

For a better understanding of the nature and objects of the invention,reference should be had to the following detailed description and to thedrawings, in which:

a glass coating to the magnetic sheet.

It has been found that extremely low magnetostriction, and hence a lownoise level, may be obtained in electrical steel sheets of orientediron-silicon alloys having thereon a coating of complexmagnesiumcontaining compounds by providing on this coating an overlyingadherent thin coating of glass having a low coefficient of thermalexpansion relative to the steel sheet so that the sheet is maintained intension after the composite sheet has cooled to room temperature. It hasbeen demonstrated that core losses are substantially reduced in thecomposite sheet of this invention. Single oriented materials in mostcases have a coating of complex magnesium containing compounds as aresult of the manufacturing process, and such a coating can be providedon double oriented materials as required.

In FIG. 1, there is shown an enlarged cross-section of a glass coatedelectrical sheet of this invention in which the various layers can beseen. The oriented magnetic steel sheet 1 has on its surface a millcoating" 2 of complex magnesium base compounds which usually is theproduct of the reaction of MgO, applied as an aqueous suspension ofmagnesia or magnesium hydroxide, with the iron-silicon sheet at anelevated temperature. The complex mill coating contains as its principalcomponents MgO, FeO and SiO The steel sheet is commonly supplied incommerce with this adherent mill coating present thereon. Thisintermediate coating 2 may in some cases include a magnesium phosphatecoating superimposed on and reacted with the mill coating. Aluminumphosphate coatings also may be applied to the steel sheet as forinstance, Al O '3P O with or without small amounts of silica and ironoxide. These comprise phosphoric acid and hydrated alumina. In othercases, this intermediate coating may be the reaction product ofmagnesium phosphate alone with the bare steel sheet. The glass coating 3is the outermost coating on the steel sheet and is well bonded to theintermediate coating 2. The glasses used for the coating 3 in carryingout the invention will bond tenaciously to the coating 2, and have a lowthermal coefficient of expansion relative to that of the steel sheet,and therefore, on cooling from annealing temperatures, contract lessthan the steel sheet and thereby hold the steel sheet in tension. Inappearance, the coated steel is a uniform grey and the coating 3 is bothvery smooth and extremely thin so that a good space factor is obtained.The coated sheet is quite flexible and the coating does not crack inbending at least until the elastic limit of the steel is exceeded. It isthus seen that the oriented steel sheet 1 has a glass coating on bothsides thereof which is effective to place the steel sheet in tension.

A suitable glass for the practice of one aspect of the invention is onethat has a coefficient of expansion of not over 8.5 X 10 /C andpreferably below 5 X l0'/C, which fuses and coats steel at a firingtemperature of below 925C and above about 700C, is a good electricalinsulator in thin coatings of the order of 0.1 mil, and is stable whenexposed to the atmosphere and liquid dielectrics such as petroleum oil.It should be noted that the iron-silicon alloy to which the glass isapplied will have a coefficient of thermal expansion of about 13 X 1O /Cat about 800C.

As one example of the glass coating 3, a family of zinc oxide glasseswhich is found to be satisfactory and forms a part of this invention,has the composition:

Constituent Weight Percent ZnO 31-60 B 0 1 1-22 PbO 10-44 SiO, 8-14 Theglasses of this composition have coefficients of thermal expansion whichare generally less than 5 X 1O' /C.

Within the broad range set forth above, a preferred composition has thecomposition:

Weight Percent Constituent (Approximate) ZnO 60 B 0 20 P 1 2 SiO; 8

Constituent Weight Percent ZnO -8 SiO, O-lO Na O 0-3 CaO 0-7 MgO 0-48210 0-5 and with optional additions of up to 1% by weight of As O up to1% by weight of V 0 up to 5% by weight of B 0 and up to 5% by weight ofFe O A somewhat narrower range of phosphate glasses within the scope ofthis invention, having coefficients of thermal expansion generally lessthan 8 X l0 /C, has the composition:

Constituent Weight Percent P 0 60-70 MnO l0- l 4 A1 0 9-l2 ZnO 4-7 SiO1.5-3.5 N620 0-2 CaO 0-1 As O 0-1 V 0 0-] Within the range of thisrestricted family of glasses a preferred glass has the composition:

Weight Percent As a further example, a family of silicate glasses hasbeen found to be particularly satisfactory for bonding wound and cutcores has the composition:

Constituent Weight Percent SiO 4555 B 0 10-14 A1 0 5-7 Na o 815 BaO10-16 CaO 5-8 P 0: up to 4 M00 up to 2 Within the above range ofsilicate glasses a preferred glass has the composition:

Weight Percent Constituent (Approximate) Si0 50 B 0 12 A1 0 6 Na O l 1-Continued Weight Percent Constituent (Approximate) BaO l5 CaO 6 It willbe understood that the above glass compositions represent the calculatedoxide content based on the raw materials employed to form the glass andthat the amounts given do not take into account losses of certainconstituents such as PbO and B 0 for example, which may be volatilizedto some extent during the fusing process, or pickup of small amounts ofother constituents from the crucible during melting, such as A1 0Therefore, the compositions given above do not necessarily represent theprecise glass analysis subsequent to fusing, although closelyapproximating such analysis.

Other glasses having the properties required may be employed inpracticing the invention.

Broadly, in practicing the invention, sheet magnetic steel having anadherent magnesium base mill coating thereon is provided with a thincoating of the order of 0.1 mil of a glass having a coefficient ofthermal expansion less than that of the steel and is heated to atemperature in the range of from 700C to 925C so that the applied glassfuses and bonds to the magnesium base coating as the steel and themagnetic sheet is simultaneously stress relieved, and on cooling themagnetic sheet is put in tension by the applied thin fused glasscoating. The glass coated magnetic sheet steel can be cut, if notalready cut, into laminations and stacked into a core. The glass coatedsteel can be wound into a spiral form and placed in a furnace and heatedto the softening point of the glass so as to bond the core turns into asolid core body. The bonded spiral wound core can be cut into twoC-shaped core portions to enable windings to be placed thereon andreassembled into a spiral core.

In practicing the process of the invention, as the glass is applied tocoils of steel sheet having the (110) [001] or [001] grain texture (orother desired grain texture) with a coating of complexmagnesiumcontaining compounds thereon, the preferred steps are: (a)scrubbing the sheet surface to remove any loose or non-adherentparticles of the coating of complex magnesiumcontaining compounds ifrequired, (b) thermal flattening, (c) dipping or otherwise providing thesteel sheet with a coating of glass slip composed of the finely dividedglass frit of the required properties suspended in a liquid such aswater or alcohol and (d) firing at a temperature of from 700C to 850C,or preferably, from 725C to 780C, to fuse the glass while stressrelieving the steel sheet.

The above glass formulations employed have a low coefficient of thermalexpansion relative to the silicon steel, and therefore, on cooling, theglass contracts less than the steel sheet and thereby places the steelsheet in tension which drastically reduces the magnetostriction andfurther reduces the strain sensitivity of the sheet.

The flattening step for coil sheet of the above process involves pullingthe sheet steel to provide a tension of about 700 psi at a temperature,for example, of 815C. Where the steel sheet is not in coil form, butrather in the form of flat sheets, the flattening step of the processoutlined above will not be necessary. Also, if the steel sheet is to beused in wound cores, the sheet is not thermally flattened. Further, thescrubbing step (which is intended to encompass any means for removingloose particles of the intermediate layer), may not be necessary in allcases, for sometimes the amount of loose particles is insignificantlysmall.

FIG. 2 shows annealing line 10in which steps (c) and (d) of the aboveprocess for treating a coil of electrical steel may be practiced. Moreparticularly, the figure shows a coil 12 of magnetic alloy sheet 13comprising, for example, silicon iron, having a mill coating or othercomplex magnesium base compounds thereon. The coil 12 rotates in aclockwise direction and the magnetic sheet 14 is drawn in the directionindicated by the arrow 17 and passes around dip roll 18 which immersesthe strip in a glass slip 21 contained in a coating tank 19. The diproll also is employed to change the direction of the sheet to a line oftravel vertically upward. As the sheet moves upwardly from the coatingtank 19, it passes between spray heads 24 which are connected toreservoir 22 by conduits 23. The reservoir 22 holds a supply of glassslip which may be continuously replenished from coating tank 19 by pump27 through the conduit 26. The spray heads 24 completely cover bothsides of the steel sheet with a thin uniform coating of the glass slip.While in the line shown in FIG. 2, two coating means are employed, i.e.,coating tank and spray heads, in some cases only one of these means isrequired.

The steel sheet in its path vertically upward from the spray heads 24passes between wiping rolls 28 which assure that the steel sheet has athin, even coating of glass slip on both sides thereof. The excess glassslip, of course, flows down the sheet 14 and back into the coating tank19. The wiping rolls 28 also are the means by which tension ismaintained on the sheet 14 during the passage through the annealingline. The sheet, continuing its vertical upward movement above thewiping rolls passes through, essentially axially thereof, an inductioncoil 32 which raises the temperature of the alloy sheet to a criticalannealing temperature relatively quickly in a short distance of travel.In the same temperature range, the glass is heated to its firingtemperature. The firing temperature is the temperature at which theglass will flow and coat the substrate within the time period availablefor the coating operation.

The sheet continues its upward movement through a narrow dead airchamber 35 which is formed by a pair of flat radiant cooling plates 34which may be liquid or vapor cooled. In the annealing line shown in thefigure, a pair of water inlets 36 and a pair of water outlets 38 areprovided so that cold water may be circulated through the cooling platesto maintain the plates at the desired low temperature. In its passagethrough the chamber 35, the glass coated steel is cooled with greatuniformity to a temperature below 400C.

After cooling, the sheet continues its upward movement to an idler roll42 about which the sheet is turned 90 to a horizontal direction ofmovement for coiling about the reel 44 which is rotated in acounterclockwise direction by a suitable drive or motor (not shown).

In some cases where high rates of sheet travel are employed, it may bedesirable to provide additional cooling of the sheet by turning thesheet to a vertically downward line of travel about the upper idler roll42.

The downward vertical line of travel would carry the sheet through asecond cooling chamber provided with means for directing an air blast onthe glass coated v magnetic sheet. Additional cooling chambers may beemployed as required to reduce the temperature of the sheetssufficiently to facilitate subsequent handling thereof.

In industrial operation, the reel 12 rotates while under a brake controlto allow the sheet 14 to uncoil and pass into the annealing line, whilethe driven wiping rolls 28 and the power applied to reel 44 determinethe tension on the sheet. It may be desirable to provide preliminaryheating of the surface of the sheet as by infrared heaters prior toentering the region of the induction coil to evaporate the fluid mediumin which the glass slip is suspended. However, if this is not done, thefluid medium will rapidly evaporate in the induction coil itself.

The induction coil 32 raises the temperature of the sheet in a narrowband by means of longitudinal flux induction heating. The sheet, as ittravels through the induction coils, reaches red heat only momentarily.This is strikingly visibly apparent, for a straight narrow hightemperature red band is visible transverse of the sheet and extends fromedge to edge.

The handling and guiding of the moving sheet is aided by the use oflongitudinal flux from the encircling induction coil because the sheetautomatically tends to take up a central position within the coil ratherthan being attracted to the inductor pole faces, as would be the case ifa transverse flux induction coil arrangement had been employed.

While the above discussion has been limited to a vertical inductionheating line which has certain advantages, it will be understood thathorizontal coating and annealing lines may be used as well and thatradiant electric or gas heating may be employed instead of the inductionheating means shown.

The improved glass coatings of this invention are not only capable oflowering the magnetostriction but are particularly adapted to be appliedover MgO or magnesium phosphate coatings or both on commerciallyproduced single oriented electrical steel. That portion of the coatingwhich is termed mill coating" is an integral part of the presentcommercial process of obtaining a single oriented material. Themagnesium phosphate, or Carlite coating as it is sometimes called, isoften superimposed on the mill coating to increase electricalinsulation. It has been found that the glass coatings when superimposedon the mill coating or on the Carlite coating, results in no degradationand sometimes even effect an improvement in the electrical losscharacteristics of the electrical steel. Certain of the glasses withinthe scope of the invention can be applied at the relatively lowtemperature of about 700 to 850C, and preferably, from 725C to 780C, toa range of temperature which is in the stress relief range for theelectrical steel sheet. The glass coatings substantially decrease thestrain sensitivity of both the magnetic properties and themagnetostriction of the single oriented materials.

Further, the glass coatings of this invention are effective when appliedin thicknesses on the order of only about 0.1 tenth to 0.3 mil oneach-side of the sheet, a matter which is of importance since the spacefactor must be taken into consideration in the design of transformers.The space factor is the ratio of the equivalent solid volume, calculatedfrom the weight and density of the steel, to the actual volume of thecompressed stack of steel sheets in an electrical steel core, determinedfrom its dimensions. Space factors greater than 94% can be obtained withthe thin glass coatings of this invention, and such high space factorvalues are eminently suitable for present transformer designs.

In the preparation of glass coatings compositions, the components of theglass composition are first melted; then the glass is fritted and ballmilled in a fluid medium to form a fine slurry. The glass mayalternatively, be dry ground and then added to the fluid medium. Thefluid medium employed may be ethyl alcohol, propyl alcohol, or anaqueous glycol solution (ethylene glycol for instance) in some cases,but generally it will be water. Water is the preferred fluid medium forcommercial operation, since it is far cheaper and safer than any otherfluid medium which would be employed.

The composition and physical properties of three representative glassesare given in the following table:

TABLE I Composition and Properties of Glass Coatings M305 PH115 LX101SiO q 50.00 2.75 8.00 3.0, (wt. 7. 12.00 20.00 P 0, (wt. 7. 66.00 A1(wt. 7:) 6.00 10.50 Na O (wt. '7!) 10.00 1.50 CaO (wt. 1) 6.00 0.75 BaO(wt. 7!) 15.00 ZnO (wt. 71) 5.50 60.00 PbO (wt. 7:) 12.00 MnO (wt. '71)12.00 M00: (wt. 71] 1.00 AS203 (wt. 71) 0.50 v.0, (wt. '71 0.50 Coef. ofThermal Expansion. X 10"/C 8.2 7.2 4.6 Deformation Temp, "C 620 490 -400Firing Temp, "C 925 760 760 Glass M-305 of the above table requires, aswill be seen, a firing temperature in air of slightly above 900C and hasa high coefficient of expansion. Although it is possible to modify theglasses in this system to obtain lower thermal expansion values, stillhigher firing temperatures would normally result. High firing temperatures i.e., above 925C, in air tend to degrade the properties of thecoated steel as to electrical losses. Glass PH] ofthe above table is aphosphate base glass and can be fired between 750 and 800C and itscoefficient of thermal expansion is somewhat lower than glass M- 305.Glass LX101, which has an extremely low thermal expansion value, is azinc oxide base glass which can also be fired in the 750 to 800C range.The silica content of this latter glass is maintained at a low level toas sure a relatively low firing temperature.

In making glass LX101 in accordance with this invention having thecomposition:

Weight Percent Constituent (Nominal) ZnO 60 B 0 PM) 12 SiO; 8

The following raw materials are weighed out in the following weightproportions:

ZnO 60 H 50 35.5 Pb SiO 14.1 SiO 5.8

The dry powdered raw materials are mixed thoroughly in a powder blenderfor several minutes and then poured into a crucible, which is preheatedto about 2,100F. The crucible is suitably made of a ceramic materialcalled Kyanite" which contains both A1 0 and SiO The crucible is placedin a furnace at about 2,100F and the contents thereof are fused. Themolten glass is stirred occasionally during the process to removebubbles and after complete fusion the glass is fined which means thatthe molten glass is permitted to stand in the furnace at temperaturewith occasional stirring to further reduce the amount of bubbles.Thereafter, the glass is poured into water or between water cooled rollswhich produces a glass frit. In the case where the glass is poured intowater, the frit is in the form of fine beads and in the case where theglass is poured between water cooled rolls the glass frit is in the formof flakes. Thereafter the frit is dried and then introduced into a ballmill with a suspending agent which may be water or alcohol such asethylene or ethyl alcohol. The frit is ground for a period oftimesufficient to produce the desired powder size; for example, a size inwhich passes through a 325 mesh screen and passes through a 100 meshscreen. When the desired particle size has been achieved, the slipsuspension is discharged from the ball mill and applied to theelectrical steel sheet.

In making the phosphate glass Pl-l1l5 the following raw materials wereused in the weight proportion list below:

NH,H,P0. 65.00 Mn P0,'7H,O 27.10 Al P0 25.10 ZnO 5.50 SiO 2.75 Na PO4.93 Ca C0 1.34 A5 0 .50 V 0 .50

The steps employed in making a slip of glass PHllS are identical to thesteps prescribed with respect to glass LX101.

The uncoated single oriented material has a very high positive A valuein the rolling direction. Most single ori ented material in the 10 to 14mil thickness range is produced with an MgO mill coating. This coatingresults in a substantial decrease in )t over bare single orientedmaterial; however, the decrease is somewhat erratic and the material isstill very strain sensitive. We have found that the glasses of thisinvention can be applied directly to the mill coating, resulting inconsistently low A values and decreased strain sensitivity.

One process for coating a coil of the single oriented mill coated"material is as follows: (a) scrub the surfaces of the sheet to removenon-adherent mill coating as required, (b) thermally flatten theannealed coil, (c) apply glass slip and dry, (d) fire at 700 to 850C inair. In the thermal flattening step, a stack of sheets sheared from thecoil is placed in a furnace at a temperature of 1,050C for 3 hours.Employing the procedure thus outlined, oriented steel sheets were glasscoated and the losses and magnetostriction of the sheets were comparedwith the same properties of bare steel sheets and sheets having a millcoating thereon, as set forth in the following example:

EXAMPLE I The following results were obtained in the rolling directionof flattened 11 mil thick single oriented matel0 rial. Glass coatingshaving thicknesses of 0.2 to 0.3 mils per sheet side were used.

TABLE 11 Fe Fe 15/60 17/60 A X Coating (w/No.) (w/No.) 151(G 17.5KG 20KGBare 10.9 15.8 20.5 Mill Coat .49 .71 0.8 2.0 5.6 Glass M-305 .50 .721.0 1.6 0.3 Glass PH115 .49 .70 0.8 1.5 0.1 Glass LX101 .48 .69 1.0 1.51.0

In the above Table 11, the results obtained with the glass coated sheetare compared with both bare sheet and mill coated sheet. Pc is the wattsloss per pound of the magnetic core at the given induction at the givencycles; 15/60 meaning 15,000 gauss at 60 cycles. KG is kilogauss. Theresults in this case indicate that the mill coated material has fairlylow A compared to bare material, however, in other tests, as set forthin Table V below, the A values obtained on mill coated material wereconsiderably higher. Glass M-305 increased losses slightly, whileglasses PH115 and LX101 were about the same as mill coated material orsomewhat lower in loss. All three glasses resulted in consistent lownegative )1 values.

The strain sensitivity of mill coated single oriented material and theeffect of the glass coatings thereon is illustrated by the followingresults obtained by test samples with the residual radius of curvature,resulting in bending stresses:

TABLE IV Pc Pc 15/100 17/400 A (x X 10') Coating (w/No.) (w/No.) 15KG17.5KG ZOKG Magnesium- 6.37 9.35 14.7 19.8 25.3 phosphate Glass PH1154.82 7.35 0.3 1.3 4.6

As will be noted from the above table, the thin single oriented materialwith a magnesium phosphate coating thereon had a very high A. The glasscoating reduced the losses substantially, far below the commonly notedloss levels in this material, and greatly decreased A.

EXAMPLE 11 Samples of single oriented electrical steel sheet were coatedwith (1) phosphate glass in water, and (2) zinc oxide glass in alcohol.The sheet was provided with coatings of the glasses which were rolled onand wiped to obtain an even coating and thereafter fired. The results inrespect to magnetostriction obtained on each of the glass-coated sheetsis compared with steel sheet having a mill coating (reaction products ofMgO) and a magnesium phosphate coating superimposed on the mill coating.The following results were obtained:

TABLE 111 Radius of Curvature Pc 15/60 Pc 17/60 A (X 10) Coating(lnches) (w/No.) (w/No.) 15KG 17.5KG ZOKG Mill Coat flat .49 .71 0.8 2.05.6 Mill Coat 72 .52 .77 5.3 9.1 12.8 Mill Coat 48 .58 .82 7.2 12.1 17.1Glass M305 48 .51 .76 1.4 4.3 7.7 Glass PH 1 15 72 .51 .73 1.1 2.0 0.2Glass PH115 48 .52 .74 1.2 3.8 7.7

The results show that the sheet is quite sensitive to TABLE V bendingstresses caused by only very small amounts of curvature in that suchstresses substantially increase 10%) G1 t losses and magnetostrtctton ofmill coated single oriasscoa mg 75x6 ZOKG ented material. The glasses onthe other hand, greatly mane h 4.0 6.5 10.8 osp ate 0.3 1.7 5.2 decreaseA of the bent samples and even reduce losses, zinc oxide 04 1'6 52 aneffect not previously observed. Comparing the losses (Pc 15/60) at aradius of curvature of 48 inches with mill coated flat sheet, the millcoated sheet with bending stresses showed at 18% increase in losses,while the glass (PHI 15) coated sheet showed only a 6% increase inlosses.

A thin gauge single oriented material (2 to 6 mils) is normallycommercially produced bare and is thereafter coated with a magnesiumphosphate coating which is fired at about 750C. This magnesium phosphatecoat- Avcragc of two samples The above results clearly indicate that theglass coatings have substantially lowered the magnetostriction of thesilicon steel. It must be observed in considering Table V that while themill coated electrical steel sheet with no additional glass coating hasa somewhat higher range of magnetostriction values in the tests than isusually experienced in this material, however, from a comparativestandpoint the glass coatings have clearly Portions of an additionalsingle oriented coil were roll coated with glasses in an annealing linesimilar to that shown in FIG. 2. The samples were all annealed with a 48inch radius of curvature therein, then flattened and tested.

TABLE VI Test On Commercial Coil-Single Oriented Material Total Coat- FeFe ing Thick- Hc Br B 15/60 17/60 A [X 10) Glass Mesh ness (mils) BendAnneal (oersteds) (gauss) (gauss) w/lb w/lb 1 l .5 G

None None None .139 10300 18200 .72 1.01 11.7 15.1 None Mill coatingNone Fired .115 13300 18500 .63 .91 12.4 17.0

no glass None 7 None 3 hr. .091 15900 18800 .51 .75 0.5 0.8

1050C. LX 101'' 400 .36 None fired .098 11700 18500 .52 .76 0.4 0.5 LXF101 60 .28 None fired .097 13300 18700 .52 .74 0.4 0.2 LXF 101 100 .36None fired .098 13100 18500 .52 .75 04 0.5 LXF 101 200 .36 None fired.096 12600 18700 .52 .75 0.4 -0.6 LXF 101A 100 .34 None fired .096 133018700 .53 .76 0.3 0.1

"Roller coated zinc oxide glass Propylenc glycol suspension of zincoxide glass EXAMPLE In It will be noted from the above table that amarked improvement in the magnetostriction is noted in all sam- Aportion of a mill coated coil of a single oriented steel sheet wascoated with a zinc oxide glass slip and fired to coat the steel and toanneal the steel sheet. The results obtained on the glass coated steelsheet are compared in the following table with steel sheet from the samecoil which had on it only a mill coating.

TABLE Vll Effect of Glass Coating on Sheet Annealed With Bend TotalThickness Hc Br B Pc15/60 Pc17/60 80 (X 10) Glass Mesh (mils) Bend(oersteds) (gauss) (gauss) w/lb w/lb 15 KG 175 KG None None .089 1570018400 .49 .72 -0.1 0.3

None 48" .098 13000 18600 .55 .77 6.1 10.0

radius Zinc Oxide" 400 .2 48" .095 11500 18600 .54 .79 1.5 4.4

radius Zinc Oxide 60 .26 48d: .094 12600 18800 .50 .73 0 .6 2.5

1'8 lUS Zinc Oxide 100 .28 48d .096 11900 18600 .53 .75 3.6 7.7

1'11 lLlS Zinc Oxide 200 .30 48" .095 11700 18700 .53 .76 0 .9 2.6

radius Zinc Oxide 100 .40 48" .097 11300 18600 .53 .75 1.7 4.6

radius Dip coated Propylene glycol addition The glass particle size wasvaried in the samples of 2 g-gg Table V1 without any apparent effect onthe results. gig 12:62 It should be noted from the above table that theZnO 57.92

losses are substantially reduced solely by the application of the glass.Of course, the magnetostriction has been reduced from high positivevalues to small negative values.

The LX101 glass used in the above tests was chemically analyzed with thefollowing results.

ZnO 57.64 B 0 1932 PbO l 1.85 SiO; 9.24

Bal. A1 0; and other impurities.

The coefficient of thermal expansion of the glass was measured and foundto be 4.6 X 10" /C.

Ba]. principally A1 0 by annealing the steel at 1200C in contact withMgO. The following Table VIII sets forth the results which were obtainedusing the pseudo mill coating just described on 12 mil double orientedsiliconiron measured in the rolling direction:

TABLE VIII Fe Fe k Coating 15/60 17/60 15KG 17.5KG 20KG Bare .82 1.1313.5 17.2 20.8 MgO .81 121 12.3 20.3 21.9 Glass M305 1.05 Glass PH115.82 1 28 3.3 5.9 7.5 Glass LX101 2.3 3.2 4.7

The above results shows that the MgO coating alone did not substantiallychange the k of the double oriented material. Because of its high firingtemperature of over 925C, glass M305 greatly increased the losses forthis test on the double oriented steel; glass PH115 did not change thelosses significantly, but did results in the substantial decrease in A.Glass LX101 also substantially reduced A. The glass coatings reduced in)tOf the double oriented material in the cross direction an equivalentamount.

The magnesium phosphate system can also be used as a base for theapplication of glass coatings to the bare double oriented silicon steelsheet material. A process suitable for coating double oriented sheetmaterial is: (a) coat with magnesium phosphate and react at atemperature of from 650 to 850C for a period of from one-half to 30minutes (b) thermally flatten the sheets at from 750C to 850C, (0) coatwith glass slip, fire at 700 to 850C. In the reaction of step (a) thehigher temperatures apply to the shorter times and the lowertemperatures apply to longer reaction periods. Double oriented materialhas been coated with glass in accordance with this process with greatlyreduced magnetostriction and good core loss values being realized.

The above description has been primarily directed to the preparation ofglass coated electrical sheets for use as laminations in stacked cores.The principles of this invention have also been successfully applied tothe manufacture of wound and cut cores of the type shown in FIG. 3 inwhich the glass coated electrical steel sheet of this invention has beenemployed in winding a core with a square window. The wound core hassubsequently been subjected to a heat treatment to the softeningtemperature of the glass which fuses the glass coating betweencontacting layers to form an integral bonded core structure while at thesame time the electrical sheet is stress relieved to reduce or removethe stresses set up in the core winding operation. The glass, inessence, provides a matrix for the core structure. In making the woundand cut cores, a glass having a firing temperature at the upper end ofthe specified range is required since it is in that range that thestress-reliefanneal of the electrical sheet can be accomplished, and, ofcourse, it is highly desirable to obtain bonding of the core and stressrelief of the sheet concurrently. In FIG. 3 of the drawings, the core 60has been cut into the two C-core halves, 61 and 62, with substantiallyplane faces 63. Whereby, when the core halves are reassembled, formingthe window 64, there is no appreciable air-gap loss between the faces.

The general process for making glass-bonded wound and cut cores is asfollows: the magnetic sheet material is provided with a thin fusedcoating of vitreous material, cooled, and then wound into a coil. Theglass coated material is subsequently wound into a core configurationthen loaded into a furnace and heated to the firing temperature with aweight or load on the core side to bring the laminations into contact tobond the core by the fused glass and to stress relieve the sheet.

One satisfactory apparatus for providing a thin fused coating of glasson the mill coated sheet is shown in FIG. 4. In the apparatus showntherein, the magnetic strip is fed through the coating line by thetake-off reel 70. The mill-coated magnetic strip 80 passes over theidler wheel 71 and into the binder trough or tank 73 around the idlerwheel 72, which is submerged in the slip (a suspension of vitreousparticles in a suitable vehicle such as amyl acetate or isopropylalcohol) in the binder tank. In the binder tank the magnetic strip isprovided with a thin coating of slip. The thickness of the coating whichthe magnetic strip acquires will depend on the speed of the magneticstrip through the binder tank and upon the consistency of the slip.Excess slip drains back into the binder tank as the strip emergesvertically from the slip.

The magnetic strip 80 passes upwardly between a set of infrared dryinglamps 74 which dry the slip coating to a powdery slightly adherentlayer. The coated magnetic strip then passes through the tube furnace 75with its heating elements 76 in which the powdry coating is fused to athin continuous layer. It should be noted that the apparatus is soconstructed that the strip surfaces do not contact any part of theapparatus while the coating is in a powdry, easily removable condition.The vitreous coating solidifies quickly on emerging from the tubefurnace and the strip passes over a series of idler rollers 77 whichdirect the magnetic strip in a downwardly path through the drive rollers91 onto the takeup reel 92. The drive rollers 91 and the take-up reel 92are driven by the power trains 95 and 96, respectively, from the driveunit 93.

While a dipping technique has been described for applying the slip tothe magnetic strip, it will be apparent that the slip may be applied byroller or by spraying. It will also be understood that the slip may be asuspension of vitreous particles in water rather than alcohol asdescribed above.

In deciding upon the glass composition to be employed in making woundand cut cores, the nature of glass must be considered. As is well known,in a glass the viscosity continuously decreases as the temperature isincreased since glass does not have a precise melting point. Theviscosity-temperature relationship of a particular glass will dependupon its composition. At about room temperature the glasses useful inmaking the magnetic cores of this invention are quite rigid withviscosities of IO poises and higher. In order to obtain the desired thincontinuous fused glass insulating coating on the surfaces of thelaminations in the coating process, the glass particles must be heatedto a fluid condition represented by a viscosity of about 5,000 poises.After the core is wound, the annealing of the magnetic strip and thesimultaneous bonding of the laminations is carried out in the softeningtemperature region of the glass for example, at a temperature of about825C, in which region the glass is in a plastic condition, having aviscosity of about 10 poises. At this viscosity the glass coating of theindividual laminations fuse and bond together when in intimate contactproduced by the contact in existence between the wound laminations oreven by pressing the laminations together. The glass bonded cores have amaximum operating temperfor all glasses at both temperatures, thoughadherence was somewhat better at the higher temperature.

A quantity of unflattened 11 mil thick mill coated, the same high gradesingly oriented steel, 1% inchs ature as high as the temperature of thedeformation 5 wide was continuously coated with glass M307 from an pointof the glass (approximately to 10 poises). alcohol slurry, and thecoating was fired by running the At the softening temperature ordeformation point, the strip through an open furnace at about 875C.C-cores glassbonded core will begin to lose its structural integ- Weiging approximately 1 lb. were wound from this rity and delamination canoccur. coated strip. These cores were annealed at various tem- Glasseswhich have been found to be particularly l0 peratures in a 90% 2, 10% H2atmosphere After suitable for the wound and cut cores are glasses whichg, the Cores were Cut With Conventional q ipcontain as a major componentoxides of silicon, and are Cores made with uncoated strip were alsoknown as silicate glasses. The composition of these silineeded Thefollowing Properties were Obtained on cate glasses may be varied widelyand innumerable varnealed and Cut (301653 iations of compositions may bemade and employed. 15 TABLE XI The following silicate glasses have beenemployed in making bonded core structures: Annealing He B10 p s 0 TABLEIX Glass Temp. (Oersted) (Gauss) (W/No.)

z 50 49 None 825 .57

3:62 2 I? Organically bonded.

Na O 11 14 25 C 6 7 These results show that low losses were obtained onBaO 15 11 P205 2 glass bonded and cut C-cores at the annealingtemperatures employed. The losses on an organically bonded and cut corewere considerably, about 10% higher.

Glass Coatings For Bonded Structures 30 The bonding technique can alsobe employed in makmg stacked cores of flat lammations. Four or five orEp p g. inches wide but more glass-coated laminations are stacked andplaced from an "nflatmned coll of 11 mil thick high grade in a furnaceto fuse the glass and thus bond the laminagle ente Steel Were CoatedWith glasses M305. tions together as a core sub-unit. The tediousassembly M307 and M308 from alcohol slurries. This steel is a f h cores,l i i b l i i can h b g g a e of Single Oriented Steel having aboutsomewhat minimized in that the bonded core sub-unit watts/1b. loss at 15kilogauss at 60 cps. The steel was groups of laminations can beassembled into a comcoated with the glass over a scrubbed mill coating.The plete core with less effort and with less likelihood of strips werebonded three at a time by annealing for 3 damage to the laminationduring the assembly operahours both at 715 and 815C in a 90% N 10% Hattion,

mosphere. It appears that some flattening of the strip There has thusbeen disclosed a relatively simple occurred, especially at the higherannealing temperamethod for reducing the magnetostriction and strainture. Samples without the glass coating were annealed sensitivity oforiented electrical steels, which produces at the same time. Thefollowing magnetic results were a novel composite electrical steelsheet. Novel glass obtained on samples bonded three at a time:compositions particularly adopted to accomplish the TABLE X AnnealingTemperature Hc B10 Pcl5/60 Pcl7/60 Glass (C) Oersteds (Gausses) (W/No.)(W/No.)

None 715 .110 18800 .54 .75

None 815 .098 18900 .50 .72

The samples without glass had better properties after desired resultshave also been presented. It will be apannealing at 815C than 715Cbecause the 715C anpreciated that the invention may be practiced in waysneal did not completely remove coil set. The 815C reother than thosedescribed herein for the purposes of sults represent about the bestEpstein values that can exemplification and pp n d0 Wish to be beobtained for this material. The glass coated and lied y the details Phereinbonded strips annealed at 715C all have essentially W claim as ouri v i Epstein properties (most likely because of tensile 1. Thecombination of an insulating glass coating stresses imparted by theglass coatings). The glass coated and bonded samples had slightly higherlosses after the 815C treatment. Good bonding was obtained overlayingelectrical steel having an adherent intermediate layer of a millcoating" comprising the reaction product of the components of thesurface of the steel 19 2i) and an oxygen containing inorganic compoundwhich 2 8 mill coating is formed during a prior heat treatment, 2 6 :5 2said glass having a coefficient of thermal expansion of less than 8.5 X10 for improving magnetostrictlon and the glass bemg charactenzed by afirmg temperature of strain sensitivity, said glass consistingessentially of: 5 between 700C and 925C.

2. The combination of claim 1 wherein composition Constituent WeightPercent is about 50% by weight of SiO about 6% by weight of sio 4545 A10 about 12% by weight of B 0 about 11% by M 0 54 10 weight of Na O,about 6% by weight of CaO, and about B o 2 6 g9 15% by weight of 830*CaO 5-8

2. The combination of claim 1 wherein composition is about 50% by weightof SiO2, about 6% by weight of Al2O3, about 12% by weight of B2O3, about11% by weight of Na2O, about 6% by weight of CaO, and about 15% byweight of BaO.